boot/data.py:create_boot_table fix OrderedDict mutated during iteration

Fixes https://github.com/openbmc/openbmc-test-automation/issues/1645

Change-Id: Ia81a5761de64c624238a5b6468d2364b955aa23c
Signed-off-by: Michael Walsh <micwalsh@us.ibm.com>
diff --git a/lib/boot_data.py b/lib/boot_data.py
index 070a0e6..abb41b7 100755
--- a/lib/boot_data.py
+++ b/lib/boot_data.py
@@ -68,7 +68,7 @@
         for boot in boot_table:
             state_keys = ['start', 'end']
             for state_key in state_keys:
-                for sub_state in boot_table[boot][state_key]:
+                for sub_state in list(boot_table[boot][state_key]):
                     if sub_state.startswith("os_"):
                         boot_table[boot][state_key].pop(sub_state, None)